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Gymnocalycium horstii (Sider Cactus)


Scientific Name

Gymnocalycium horstii Buining

Common Names

Spider Cactus

Scientific Classification

Family: Cactaceae
Subfamily: Cactoideae
Tribe: Trichocereeae
Genus: Gymnocalycium


Gymnocalycium horstii is a globular cactus with spines that are curved back towards the body. It grows up to 10 inches (25 cm) in diameter, usually offsetting over time, creating interesting specimens. Flowers are white, pale pink, pink, or pale purplish, up to 4 inches (10 cm) long and with an equal diameter.

Gymnocalycium horstii (Sider Cactus)

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USDA hardiness zones 10a to 11b: from 30 °F (−1.1 °C) to 50 °F (+10 °C).

How to Grow and Care

Some Gymnocalyciums are shade-seeking in the wild, among shrubs or grasses, while others grow completely exposed. Therefore, some will need a light shading from the sun in the hottest months, but to overdo, this will result in the loss of flowers.

The potting medium's balance should be sufficient to allow good drainage so that the plants do not sit in soggy soil for more than a day or two after watering.

Watering in the summer months, while the plants are growing well, can be frequent (weekly for small plants in small pots), but always allowing the compost nearly to dry out before rewatering. Watering in the winter months at all is unwise and certainly not necessary. The difficult times are spring and autumn.

Those species which produce offsets can be readily propagated by cuttings. Gymnocalycium seed germinates well when fresh and will keep for a few years if stored in cold conditions. See more at How to Grow and Care for Gymnocalycium.


Gymnocalycium horstii is native to Uruguay, eastern Paraguay, southern Brazil, and northeastern Argentina.


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